Clay brick manufacture - Construction Industry Development Board

Provided that a sand yields a smooth, plastic and cohesive mix, its quality, based on “water demand”
can be determined by the following test.
The quantities used should be weighed on a kitchen scale that is accurate, and the test should be
carried out on a smooth impervious surface. It is also important that the sample used is fairly
representative of the bulk supply.
Procedure:
• Dry out a wheelbarrow full of sand to be tested.
• Weigh 5 kg cement and 25 kg of dry sand. Measure 5 litres, 1 litre and 1,5 litres water into separate
containers.
• Mix the cement and sand until the colour is uniform.
• In succession, mix in each of the volumes of water (5 litres, 1 litre and 1,5 litres) until the mix
Then:
reaches a consistency suitable for plastering.
• If 5 litres is enough – the sand is of “good” quality
• If 5 litres + 1 litre is enough – the sand is of “average” quality
• If 5 litres + 1 litre + 1,5 litres is enough – the sand is “poor”
• If more than 7,5 litres is needed – the sand is “very poor”.
A “good” or “average” sand should be used for mortar in walling below the damp-proof course.
5.4.5 Mortar plasticisers
Mortar plasticisers exercise a desirable effect on the workability and plasticity of the mortar in which
they are used. Generally, the admixtures have no effect on setting time (they do not accelerate or
retard the mortar setting) but may cause air entrainment.
The use of mortar plasticisers is optional. Their effectiveness varies with the quality of sand, the
composition of the cement, its fineness, the water-cement ratio, temperature of the mortar, volume of
plasticiser and other factors or site conditions.
5.4.6 Pigments
Pigments may be used to colour mortar, with the dosage depending on the specific colour required.
The recommended limit on mineral oxide content is 7% of common cement content. Pigmented mortar
with face brickwork can change the appearance of a building dramatically.
5.4.7 Ready-mixed mortar
Ready-mixed mortar with an extended board life has been successfully used over a number of years.
Ready-mixed mortar has advantages of convenience on site as it is delivered at a consistency ready
for use. Usually it is delivered in ready-mix trucks or containers. It is stored in containers on site in a
protective manner that minimises loss due to evaporation and protects the mortar from freezing in
cold weather. No other materials or admixtures are added on the site.
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